Browsing by Author "Piitulainen, H."

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    Older adults show elevated intermuscular coherence in eyes-open standing but only young adults increase coherence in response to closing the eyes
    (WILEY-BLACKWELL, 2020-06) Walker, S.; Piitulainen, H.; Manlangit, T.; Avela, J.; Baker, S. N.; Department of Neuroscience and Biomedical Engineering
    New Findings: What is the central question of this study? Can a 14-week strength-training programme modify intermuscular coherence levels during bipedal standing tasks with eyes open and eyes closed and reduce age-related differences? What is the main finding and its importance? Older adults had more prominent common input over 4–14 Hz with eyes open, but during the eyes-closed task the young adults were able to further enhance their common input at 6–36 Hz. This indicates that young adults are better at modulating common input in different motor tasks. Abstract: Understanding neural control of standing balance is important to identify age-related degeneration and design interventions to maintain function. Here, intermuscular coherence between antagonist muscle pairs around the ankle-joint during standing balance tasks was investigated before and after strength training. Ten young (18–31 years; YOUNG) and nine older adults (66–73 years; OLDER) stood on a force plate for 120 s with eyes open followed by 120 s with eyes closed before and after 14 weeks of strength training. Postural sway was quantified from centre-of-pressure displacement based on 3-D force moments. Electromyography (EMG) was recorded from the gastrocnemius medialis (GM), soleus (SOL) and tibilais anterior (TA) muscles of the right leg. Coherence between rectified EMG pairs (GM–TA, SOL–TA) was calculated for each 120 s epoch separately. Postural sway was lower in YOUNG compared to OLDER in eyes-open (6.8 ± 1.3 vs. 10.3 ± 4.7 mm s −1, P = 0.028) and eyes-closed (10.9 ± 3.1 vs. 24.4 ± 18.3 mm s −1, P = 0.032) tasks. For both muscle pairs, OLDER had more prominent common input over 4–14 Hz with eyes open, but when the proprioceptive demand was enhanced in the eyes-closed task the YOUNG were able to further enhance their common input at 6–36 Hz (P < 0.05). Strength training reduced the instability from closing the eyes in OLDER but did not alter coherence. This may highlight a greater functional reserve in YOUNG than in OLDER and possible emerging proprioceptive degeneration in OLDER. However, the findings question the functional role of coherence for balance.
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    Rats bred for low aerobic capacity become promptly fatigued and have slow metabolic recovery after stimulated, maximal muscle contractions
    (2012) Torvinen, S.; Silvennoinen, M.; Piitulainen, H.; Närväinen, J.; Tuunanen, P.; Gröhn, Olli; Koch, L.G.; Britton, S.L.; Kainulainen, H.; Department of Neuroscience and Biomedical Engineering
    AIM Muscular fatigue is a complex phenomenon affected by muscle fiber type and several metabolic and ionic changes within myocytes. Mitochondria are the main determinants of muscle oxidative capacity which is also one determinant of muscle fatigability. By measuring the concentrations of intracellular stores of high-energy phosphates it is possible to estimate the energy production efficiency and metabolic recovery of the muscle. Low intrinsic aerobic capacity is known to be associated with reduced mitochondrial function. Whether low intrinsic aerobic capacity also results in slower metabolic recovery of skeletal muscle is not known. Here we studied the influence of intrinsic aerobic capacity on in vivo muscle metabolism during maximal, fatiguing electrical stimulation. METHODS Animal subjects were genetically heterogeneous rats selectively bred to differ for non–trained treadmill running endurance, low capacity runners (LCRs) and high capacity runners (HCRs) (n = 15–19). We measured the concentrations of major phosphorus compounds and force parameters in a contracting triceps surae muscle complex using 31P-Magnetic resonance spectroscopy (31P-MRS) combined with muscle force measurement from repeated isometric twitches. RESULTS Our results demonstrated that phosphocreatine re-synthesis after maximal muscle stimulation was significantly slower in LCRs (p<0.05). LCR rats also became promptly fatigued and maintained the intramuscular pH poorly compared to HCRs. Half relaxation time (HRT) of the triceps surae was significantly longer in LCRs throughout the stimulation protocol (p≤0.05) and maximal rate of torque development (MRTD) was significantly lower in LCRs compared to HCRs from 2 min 30 s onwards (p≤0.05). CONCLUSION We observed that LCRs are more sensitive to fatigue and have slower metabolic recovery compared to HCRs after maximal muscle contractions. These new findings are associated with reduced running capacity and with previously found lower mitochondrial content, increased body mass and higher complex disease risk of LCRs.